It is well known to those skilled in the art that aromatic hydrocarbons are a class of very important industrial chemicals which find a variety of uses in petrochemical industry. It is also well known to those skilled in the art that catalytically cracking gasoline-range hydrocarbons produces aromatic hydrocarbons such as, for example, benzene, toluene, and xylenes, which are hereinafter collectively referred to as BTX or C.sub.6 to C.sub.8 aromatic hydrocarbons, in the presence of catalysts which contain a zeolite. The product of this catalytic cracking process contains a multitude of hydrocarbons including unconverted C.sub.5 + alkanes, C.sub.5 + alkenes, C.sub.5 + cycloalkanes, or combinations of two or more thereof; lower alkanes such as methane, ethane, and propane; lower alkenes such as ethylene and propylene; and C.sub.9 + aromatic compounds having 9 or more carbon atoms per molecule. Recent efforts to convert gasoline to more valuable petrochemical products have focused on improving the conversion of gasoline to more valuable aromatic hydrocarbons in the presence of zeolite catalysts.
Aromatic hydrocarbons having 8 carbon atoms per molecule which can be derived from the above-described catalytic cracked gasoline, catalytic reformate, pyrolysis gasoline, or combination of two or more thereof generally comprises a mixture of ethylbenzene and xylenes. Among the xylenes, p-xylene is economically most valuable. Ethylbenzene is undesirable because it is less valuable economically than a xylene. Therefore, ethylbenzene must be either physically removed or chemically converted to other more valuable chemicals. However, it is difficult to physically separate ethylbenzene from p-xylene because ethylbenzene and p-xylene have very close boiling points and molecular sizes. An alternative to physical separation of ethylbenzene from p-xylene is chemical conversion of ethylbenzene to xylenes and/or other economically more valuable aromatic products.
Commercial processes for conversion of ethylbenzene, which requires the presence of a xylene, generally either insufficiently convert ethylbenzene to xylenes or do not retain the xylenes in the feed stream or both. Therefore, there is an ever-increasing need to substantially convert ethylbenzene or reduce the content of ethylbenzene and, in the mean time, retain most xylenes in the feed stream.